new feature for Amarok 2.0 

New Music search engine which uses an algorithm for generating unique acoustic fingerprints. From these fingerprints, songs can be identified by their acoustic signature regardless of differences at the digital data level (file format, data compression rates, etc). While the technology required to create fingerprints is proprietary, identifying tracks against the existing fingerprint database can be done freely through the MusicDNS service. 

Amarok also features music analysis technology, recognising meaningful (to humans) musical attributes, so that the software is able to identify tracks that are perceivably similar. 

similar programs
MusicIP
http://www.musicip.com
http://en.wikipedia.org/wiki/MusicIP

and

Mufin Music Finder
http://www.mufin.de

other feature request
the plugin look @ last.fm and make own playliste (with music on harddisk) mixed music direction from last.fm